static-静态方法和工具类

• 什么叫静态方法

  特点和调用方式

  • 工具类

    定义：帮助我们做一些事情的，但是不描述任何事物的类

    1. 已经学习过的类

    2. 工具类的使用规则

    3. 练习

       实操

       类--ArrayUtil

       package a02staticdemo2;
       public class ArrayUtil {
           //私有化构造方法
           //目的：为了不让外界创建他的对象
           private ArrayUtil(){}
       
           //需要定义为静态，方便使用
           public static String printArr(int[] arr){
               StringBuilder sb = new StringBuilder();
               sb.append('[');
               for (int i = 0; i < arr.length; i++) {
                   if (i<arr.length-1){
                       sb.append(arr[i]).append(",");
                   }else if (i==arr.length-1){
                       sb.append(arr[i]).append("]");
                   }
               }
               return sb.toString();
           }
           public static double getAverage(double[] arr){
               double sum = 0;
               for (int i = 0; i < arr.length; i++) {
                   sum = sum + arr[i];
               }
              return sum / arr.length;
           }
       }
       

       测试--TestDemo

       package a02staticdemo2;
       public class TestDemo {
           public static void main(String[] args) {
               //测试工具类中的两个方法
               int[] arr1 ={1,2,3,4,5};
               String str = ArrayUtil.printArr(arr1);
               System.out.println(str);//[1,2,3,4,5]
       
       
               double[] arr2 = {1.1,2.2,3.3,4.4,5.5};
               double average = ArrayUtil.getAverage(arr2);
               System.out.println(average);//3.3
           }
       }
       

    4. 练习2

       实操

       工具类--studentsArrayUtil

       package a03staticdemo3;
       import java.util.ArrayList;
       public class studentsArrayUtil {
           private studentsArrayUtil(){
       
           }
       
           public static int age(ArrayList<students> ast){
               int sum = 0;
               for (int i = 0; i < ast.size(); i++) {
                   int age = ast.get(i).getAge();
                   if (age>sum){
                       sum  = age;
                   }
               }
               return sum;
           }
       }
       

       学生类--students

       package a03staticdemo3;
       public class students {
           private String name;
           private int age;
           private String gender;
       
           public students() {
           }
       
           public students(String name, int age, String gender) {
               this.name = name;
               this.age = age;
               this.gender = gender;
           }
       
           public String getName() {
               return name;
           }
       
           public void setName(String name) {
               this.name = name;
           }
       
           public int getAge() {
               return age;
           }
       
           public void setAge(int age) {
               this.age = age;
           }
       
           public String getGender() {
               return gender;
           }
       
           public void setGender(String gender) {
               this.gender = gender;
           }
       }
       
       

       测试--studentsTest

       package a03staticdemo3;
       import java.util.ArrayList;
       import java.util.Scanner;
       
       public class studentsTest {
           public static void main(String[] args) {
               Scanner sc = new Scanner(System.in);
               ArrayList<students> ast = new ArrayList<>();
               for (int i = 0; i < 3; i++) {
                   System.out.println("请输入学生姓名");
                   String name = sc.next();
                   System.out.println("请输入学生年龄");
                   int age = sc.nextInt();
                   System.out.println("请输入学生性别");
                   String gender = sc.next();
                   students st = new students(name,age,gender);
                   ast.add(st);
               }
               int age = studentsArrayUtil.age(ast);
               System.out.println(age);
           }
       }